Bonded sawdust filter medium



Oct. 30, 1956 s. w. BRIGGS BONDE SAWDUST FILTER MEDIUM Filed Aug. 12,1943 ame/whom Jaw-mwa( h( 59/665 ATTOR N EY BONDED SAWDUST FILTER MEDIUMSouthwick W. Briggs, Bethesda, Md. Application August 12, 1948, SerialNo. 43,797

18 Claims. (Cl. 210-205&

This invention relates to the art of filtration of fluids and moreparticularly to a novel filter medium of bonded sawdust and a method ofmanufacturing the same.

The widespread use of internal combustion engines has created a demandfor a filter for the removal of impurities from the oil used in thelubrication of the engines. The filters should be cheap and compact andstill have the ability to remove large quantities of sludge from the oilbefore becoming plugged, and yet allow a high rate of flow of the fluidtherethrough. Ordinarily, a high dirt Capacity may be obtained only if alarge portion of the impurities are deposted within the filter mediumrather than merely on its inlet surface. However, it is essential thatthe filter remove the irnpurites from the fluid. It has generally beennecessary to provide rather complicated, expensive structures to obtainboth a high Capacity and effective removal of impurities.

It is essential that filters for widely used equipment such asautomobiles be rugged and capable of withstanding the rough handlngwhich it encounters in garages and in shipment. Of course, the filtermaterial must also be resistant to any solvent or corrosive action ofthe fluid being filtered and the temperatures existing during thefiltration operation. The filters usually available having a highcapacity have little physical strength and must be handled with care.This is especially true of filter cartridges comprising a stack of discsin which a harness must be provided to maintain the Cartridge in atightly compressed condition, thereby increasing the cost of the filter.

It is an object of this invention to provide a filter medium preparedfrom sawdust bonded into the desired shape with a resin.

Another object of this invention is to provide an eflicient filtermedium having a high dirt Capacity.

A further object of this invention is to provide a filter medium ofsawdust bonded with a resin to form a porous block having a highmechanical strength.

Still another object of this invention is to provide a filter medium forthe filtration of lubricating oils capable of withstanding thetemperatures and materials encountered in the filtration of lubricatingoils for internal combustion engines for extended periods.

It is also an object to provide a highly efiicient filter medium whichmay be prepared at a low cost from materals readily available in largequantities.

With these and other objects in view, as will become apparent in thefollowing description, this invention resides in the bonding of sawdustwith a resin to form a strong porous, rigid block through which a fluidmay be passed for the removal of impurities.

In the drawings:

Figure 1 is a vertical cross-sectional view of a filter constructedaccording to this invention; and,

Figure 2 is a Vertical cross-sectional view of a modified form of thefilter mass prepared according to this invention.

* In the preparation of filter material according to this Patented Oct.30, 1956 invention, sawdust from any Wood-working operation producing amaterial of the proper particle size may be employed. A typical sawdustwhich may be employed is designated as ZO-F and is prepared by passingordinary sawdust through a 20 mesh screen to remove the large chips. Thematerial passing through the screen is a wide cut ranging fromrelatively large particles to very fine material. The fine materialincreases the strength of the bonded filter material, but the amountpresent must be limited to retain the proper porosity of the finishedblock. satisfactory filter materials have been prepared from pine, fir,oak, and briar sawdusts and undoubtedly may be prepared from otherWoods.

In order to obtain accurate control of the properties of the filtermedium prepared according to this invention it will generally bedesirable to use sawdust having a controlled particle size. While thematerial which is merely screened through a 20 mesh screen issatisfactory, the properties of the resultant products will vary betweenrather wide limits because of the variation in the size and quantity offines. It is preferred, therefore, to use a mixture of a number of cutsof the sawdust having fixed minimum as well as maximum particle sizes.For example, a mixture of sawdust in which of the material has aparticle size of 20-60 mesh and 10% of the material has a particle sizeof 922- mesh will produce a filter medium having propertiesapproximating that of 20-F sawdust.

The sawdust used is essentially granular in shape, and when subjected topressure in the manufacture of the block merely packs and does not flowto form a dense continuous mass. In contrast with fine fibrousparticles, the sawdust allows the formation of a porous material throughwhich a liquid may be readily passed, rather than a dense, imperviousmass of plastic.

The sawdust is mixed With a resin which binds the sawdust into a strong,coherent, unitary mass of the desired shape. The granular shape of thesawdust particles does not permit interlacing of the particles in themanner that fibers are interwoven in the manufacture of paper;consequently, the bonded block of sawdust depends on the resin for itsphysical strength. Resins which have been found especially satisfactoryare phenol-formaldehyde, phenol furfural, melamine formaldehyde,resorcinol formaldehyde, lignin, and mixtures of urea-formaldehyde andmelamine.

Generally, any resin which becomes tacky before setting and will bindthe sawdust into a strong mass is satisfactory, but the particular resinused will depend upon the use contemplated for the filter. In thefiltration of lubricating oils for internal combustion engines it isnecessary that the resin employed to bond the sawdust be capable ofwithstanding temperatures of about 200 F. and water at that temperaturefor extended periods. The hot press or high-temperature setting resinsof the types listed above and the intermediate temperature settingresins are excellent for this use. In most cases the cold settingresins, thermoplastic, and the natural occurring resins such as Manilla,Coumar, etc. will soften at temperatures below 200 F. and are notsatisfactory for the filtration of hot lubricating oils. However, theymay be used for filtering cold fluids provided they will withstand theChemical and solvent action of the fluid.

In the preferred method of preparing the filter medium the sawdust ismixed with a dry resin powder to avoid the formation of a Sticky mass,and to extend the time available for working the mixture. The dry resinpowder and sawdust mixture may be stored overnight or longer withoutdanger of the resin setting. A phenol-formaldehyde resin which may bereadily obtained in the powder form and is especially suitable for thispurpose is Amberlite, P. R. 14, prepared by the Resnous Products &

Chemical Co. of Philadelphia, Pennsylvania. Dry resin powderrangingfromabout 15% to amaximum of25-% of the weight of the sawdust ismixed with the sawdust in a conventional dough mixer until the resin isuniformly distributed throughout the'sawdust. The dry mixture is thenmolded under one-hundredpounds per square inch pressure into the desiredshape. Itis-baked, while held at aconstant Volume, at a-temperatureof"300 F. for two hours and forty minutes to set the resin permanently.The exact time and temperature of heating will, of course, depend on theparticular resin employed. The Amberlite P. R. 14 resin may be set attemperatures as low as 180 F.

A preferred resin, because of its excellent physical properties and' lowcost, is a resin' prepared from phenolfurfural. It may be used in a drycondition and sets at a temperature of 300-350 F. A resin of this typeis prepared by the Borden Co., and identified by S-2l5l.

The filter medium may also be prepared by mixing the sawdust with asolution of the resin to forma wet mix which may be molded into thedesired shape. It is then not necessary to mold the wet mix underpressure. The resin solution should contain 50-75% resin to provide atacky solution giving a block with sufl'icient strength prior to heatingto hold the molded mixture of resin and sawdust in the desired shapeduring the subsequent heating operation. A concentrated resin solutionof 50-75% is also necessary to prevent migration of the resin to thesurface of the molded shape during the heating to set the resin.Although the resin solutions are concentrated, it is necessary toincrease the heating period to vaporize the solvents prior to setting ofthe resin.

The solvent employed in the preparation of the resin solution willdepend on the particular resin used. Forexample, the phenol-formaldehyderesins may be dissolved in water before setting. Lignin may be dissolvedin an 8% aqueous ammonia solution or a furfural alcohol solution.

When the filter block is not molded under pressure and baked while heldat constant Volume, the weight of the resin in the mixture must beincreased to approximately 50% of the weight of the sawdust to obtain ablock having sufiicient physical strength to allow it to be handled.This is in contrast with the l5-25% of the weight of the sawdust whichproduces blocks of satisfactory physical strength when the dry resin sawdust mxture is molded under pressure. If the mixture of sawdust andresin is not molded under pressure, a more open block is formed and itthen becomes necessary to use a sawdust having a finer particle size toobtain the desired filtration.

A filter block four inches in diameter and six inches high having around hole one and one-half inches in' diameter extendng axiallytherethrough was prepared from a dry mix of 20-F sawdust and anintermediate setting temperature phenol-furfural resin, by the methoddescribed above, using dry resin powder. A lubricating oil was filteredthrough the block until the block became plugged. The block removedapproximately 800 grams of sludge from lubricating oil before plugging.About 75-80% of the sludge was deposited within the block and theremainder formed a coating on the inlet surface of the block. Eventhough most of the impurities were deposited within the filter block,the block failed when the lubricating oil would no longer pass throughthe block because of the sealing of its inlet surface.

A filter block of the same size as that described above, prepared from90% of a 20-60 mesh cut of oak sawdust and of 92-110 mesh cut of whitepine sawdust, removed Substantially the same amount of sludge from thelubricating oil as for the 20-F sawdust. The total Capacity of the blockwas Substantially unchanged and the proportion of the sludge depositedwithin the block.

remainedthe same. However, a block four inches in diameter and sixinches high having a one and one-half inch-holethrough the-center,prepared from an "artificial' sawdust prepared from 50% of 20-60 meshmaterial and 50% of 92-l10 mesh material, and tested in the same manneras the block previously described, only removed grams of sludge from thelubricating oil before it became plugged. Substantially all of thesludge removed from the lubricating oil was deposited on the surface ofthis block.

Another block' having the same dimensions as those described above wasprepared from a sawdust made up of 75% 20-60 mesh material and 25%92-110 mesh material. This block removed 250 grams of sludge from theoil before becoming plugged'. Here again, substantially all of thesludge was deposited on the inlet surface of the block.

A filter prepared according to this invention is illustrated in Figure 1of the drawings having a casing 1 closed at its upper end by a cover 2.An inlet 3, is located in the lower end of the casing for theintroduction of the unflltered fluid into the casing 1. An outlet 4 alsopasses through the lower end of thecasing 1 for the discharge' of 'theclarified fluid from the filter. The casing may be provided with aclean-out plug 6 for the removal of sludge 'which accumulates in thebottom of the casing.

A center' tube 7 is Secured to the outlet 4 in a fluid tight manner andextends upwardly toward the top of the casing 1; A flange 8 is attachedto the center tube 7 near its junction with the outlet 4. A threadedcollar 9 'is welded in the upper end ofthe center tube 7 for engagementwith a hollow bolt 10 passing through the cover z of 'the filter to holdit tightly in place during the operation of the filter. Leakage of thefluid being filtered between the casing 1 and the cover 2 during thefiltering operation isprevented by a gasket 11 underneath the head onthe: bolt 10 and a second gasket 12 on the upper edge of the casing 1.

The flange' 8 supports a tubular filter Cartridge 13 of bonded sawdust,prepared by the method described herein,

in a position surrounding the center tube 7 of the filter.

The filter cartridge 13 is held firmly in place on the flange 8 by anupper flange 14 which is movable along the bolt 10. The flange 14 isurged downwardly against the 'upper end of the filter cartridge 13 by acompressed helical spring 15 bearing at its upper end against the lowersurfacetof-th'e cover 2 and its lower end against a gasket 16 of scalingmaterial on the upper surface of flange 14.` The gasket 16 is pressedagainst the bolt 10 by the springto prevent flow of fluid along theouter surface of the bolt. Ordinarily, the filter cartridge 13 willbeseparated' from the flanges 8 and 14 by gaskets 17 and 18 respectively,which prevents leakage of the unfiltered fluid pastthe ends of thefilter block 13.

The center tube 7 is apertured at 19 along its length between the flange8 and the collar 9 to permit flow of the filtered fluid discharged fromthe inner surface of the filter block 13'. In some nstances, it may bedesirable to-provide a pressure release mechanism indicated* by the port20 providing access for the unfiltered fluid from the inlet 3 to thecenter of the hollow bolt 10. Flow through the port 20 is prevented by aball 21 urged against a valve 22 by a compressed spring 23 within thehollow bolt 10.

In operation, the fluid tobe filtered enters the inlet 3 of the filtercasing 1. The fluid then passes radially through the filter block 13 tothe apertures 19 on the center tube. As the fluid passes through thefilter block, the sludge and othermpurities are effectively removed andthe fluid entering the center tube 7 is clarified. The clarified fluidthen passes from the center tube 7 to the outlet 4 to the point of use.

Since the failure of the filter block, in most instances, is the resultof plugging it s inlet surface, the shape of the` filter bloclemay* bemodified in the manner illustrated in Figure 2 of the drawings toincrease its capacity. In this form of the invention, a block 25, aftermolding and setting, is passed over gang saws and rotated thereon to cuta series of grooves 26, separated by ridges 27, in the -outer surface ofthe block. The total surface area is greatly increased and acorresponding increase in total dirt capacity of the filter block isobtained.

In order to prevent plugging of the inlet surface, it may be desrable toconstruct a filter Cartridge having a highly porous section in the inletregion and a more dense section near the outlet. For example, in thepreparation of a tubular filter cartridge for outside to insidefiltration, a sleeve may be inserted in the mold between its inner andouter surfaces. The space within the 'sleeve is then filled with amixture of relatively fine sawdust and resin, and the space surroundingthe sleeve is filled with a mixture of coarse sawdust and resin. Thesleeve is then withdrawn and the filter block is molded in the mannerherein described to produce an eflicient filter cartridge having aporous inlet area.

A novel filter medium capable of efficent Clarification of lubricatingoils and which may be prepared at a low cost has been described herein.The new material i-s resistant to continued action of hot water forextended periods. The particles of sawdust are held firmly in place bythe resin to give a block which does not shrink. Moreover, migration,classfication, and packing of the sawdust particles are prevented,thereby preserving the eflicient filtering properties of the filtermedium throughout its period of use.

While this invention has been described in detail with respect tospecific compositions and structure, it is to be understood that theconcept of this invention is not limited to those details, but islimited only by the scope of the appended claims.

I claim:

1. A method of manufacturing a filter medium comprising mixing sawdustwith a synthetic resin, molding the mixture of sawdust and resin to thedesired shape, and heating the molded sawdust at substantially constantVolume to set the resin and form a unitary porous mass of sawdustparticles bonded with the resin.

2. A filter device comprising a filter casing having an inlet and anoutlet, a porous block of sawdust bonded with a resin, and meansdirecting the fluid to be filtered from the inlet through the porousblock to the outlet.

3. A filter device comprising a filter casng having an inlet and anoutlet, a porous block of sawdust bonded with a resin having a softeningtemperature above 200 F., and means directing the fluid to be filteredfrom the inlet through the porous block to the outlet.

4. A filter device comprising a filter casing having an inlet and anoutlet, a porous block of sawdust having a maximum particle size of 20mesh bonded with a resin, and means directing the fluid to be filteredfrom the inlet through the porous block to the outlet.

5. A filter device comprising a filter casing having an inlet and anoutlet, a porous block of sawdust bonded with about 15-50% of asynthetic resin having a softening temperature above about 200 F. andmeans directing the fluid to be filtered from the inlet through theporous block to the outlet.

6. A filter device comprising a filter casing having an inlet and anoutlet, a porous block of sawdust bonded with a resin, and meansdirecting the fluid to be filtered through the block, said block havinga section near the outlet formed from fine sawdust and a section nearthe inlet formed from coarse sawdust Whereby the dirt capacity of thefilter block is increased.

7. A filter mass comprising sawdust particles bonded together throughoutthe mass with a layer of a thermosetting resin on the individualparticles binding adjacent particles to form a rigid permeable mass.

8. A filter mass comprising sawdust particles bonded together with adiscontinuous phase throughout the mass of a resin to form a rigidpermeable mass.

9. A filter mass comprising sawdust particles, and a layer of resin onthe individual particles binding adjacent particles at substantiallytheir areas of contact to form a rigid permeable mass.

10. A filter mass -as set forth in claim 7 in which the thermosettingresin constitutes approximately 15 to 50% by Weight of the filter mass.

11. A filter mass as set forth in claim 7 in which the thermosettingresin constitutes approximately 15 to 25% by weight of the filter mass.

12. A filter mass comprising sawdust particles bonded togetherthroughout the mass with a layer of a resin having a softeningtemperature above about 200 F. on the individual particles bindingadjacent particles to form a rigid permeable mass.

13. A filter mass as set forth `in claim 7 in which the sawdustparticles have a maximum size of about twenty mesh.

14. A filter mass as set forth in claim 7 in which the thermosettingresin is selected from the group consisting of phenol-formaldehyde,resorcinol-formaldehyde, phenol-furfural, melamine-formaldehyde, lignin,and ureaformaldehyde fortified With melamine.

15. A filter mass 'as set forth in claim 7 in which the resin isphenol-formaldehyde.

16. A filter mass as set forth in claim 7 in which th resin isphenol-furfural.

17. A filter mass as set forth in claim 7 in which the resin ismelamine-formaldehy-de.

18. A mass produced unitary integral filter body comprising a unitaryblock of fibers surface bonded to each other by a thermosetting resincured in situ and constituting an open porous structure of at least 60%porosity and of a strength and brittleness permitting the same to besawed cleanly, said body havi-ng a series of parallel flanges defined bysaw cuts extending from the inlet side of the block towards but short ofthe outlet side whereby said flanges are all integrally connectedtogether at their inner ends.

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